In my head, I thought of Rainbow meeting En Sabuh Nur and his sister who she becomes comrades. And is forced to witness En Sabuh Nur become Apocalypse and helps imprison him. And when he is freed through using both sides of the supers, he seems revenge on Rainbow. And he does so by forcing her to witness many suffer and die; mocking how her refusal to kill his pawns Twylight, Tony Stark, Magneto, Jonah Jameson, the Kingpin, William Stryker, Bolivar Trask, Robert Kelly, Rarity, Applejack, the Punisher, Rogue, the Chameleon, Lieutenant-General Thunderbolt Ross, General Ryker, Rhodes, SWORD, Warrington, and Nick Fury help in his return. And one song can be sung by them; similar to The Plagues from Prince of Egypt.

Apocalypse be the X-Men rogue I wish the MLP meet the most. Gen 4 and Gen 5. The oldest and darkest mutant. Able with psychic powers, super-strength, super-speed, a healing fator, super-intelligence, technoparthy, sizeshifting, shapeshifting, teleporting, and forcefield-forging. And a master puppeteer.
It rock if he was the very mastermind behind the Avengers Cyvyl War to arrange his release from his ancient prison, with AMgneto and Tony Stark as his biggest pawns. And Spider-Man reveal as the Chosen One to lead the Avengers to victorya gainst him with help froM Galactus and the Infinity Stones.
If the MLP ones got invovle, Apocalypse can use the Marer Do Well and Walking Dead hoaxes and Twylight’s gambit with Queen Novo’s gem and betraying the CMC for Cozy Glow as wella s her Lesson Zero sin to show her hypocrisyand to try and tmept a certain Wonderbolt to kill ehr. But it rock if the Wonderbolt refuse; and if she said how Spider-Man, Professor X, Shang Chi, the Black Panther, the Silver Surfer, MJ, Wolverine, Jean, and Thor prove more worthy to be gods than him.